Environmental variability during the last three millennia in the rain shadows of central Mexico

The last three millennia have been characterized by global temperature oscillations of around one Celsius degree, and high frequency variability on precipitation. Two main temperature anomalies have been reported worldwide, the Medieval Warm Period (MWP) and the Little Ice Age (LIA), characterized by higher and lower than average temperatures, respectively. Precipitation variability has been mostly associated with El Niño anomalies in the Equatorial Pacific. These global variability modes have been modulated by regional factors such as sea surface temperatures and their interaction with continental landmasses. Understanding regional responses to these anomalies would shed light on ecosystem response to environmental variability, a paramount tool for conservation purposes on the light of modern climate change. Here we present a 3,000-year sedimentary record from Lake Metztitlán, located in a Biosphere Reserve under the rain shadow of the Sierra Madre Oriental. Cladoceran and geochemical analyses were used to reconstruct lacustrine dynamics through the time period encompassed by the record. Our record points to highly dynamic lacustrine systems, coupled with global and regional climatic variability. In Metztitlán, the MWP was associated with low lake levels and a high torrentiality of the precipitation reflected in high-frequency peaks of detrital material. The LIA was associated with an enlarged water body, probably as a result of lower evapotranspiration. Overall, global climatic variability resulted in high variability of regional precipitation and detrital input in the Metztitlán region, in turn associated with changes in lake morphometry and depth. Our record highlights the vulnerability of the area to changes in sea surface temperature of the Gulf of Mexico, and to changes in the frequency of El Niño events. Although the effects of global climate change in the region are inescapable, our results emphasize the importance of controlling anthropogenic activities as an additional source of pressure on the regional ecosystems.